On Wed, May 9, 2012 at 7:51 PM, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
> On Tue, May 8, 2012 at 8:20 PM, Mikulas Patocka <mpatocka@redhat.com> wrote:
>>> Switching it to zero and testing that things still work would be appreciated.
>> It works, but there is plenty of interrupt controllers on PC-RISC and I
>> can only test it on C8000 with IO-SAPIC. I don't know if irq 0 is used on
>> some PA-RISC interrupt controller. It would be best if James Bottomley
>> tests it on his set of machines.
>
> Heh. It sounds like we have more PA-RISC machines than we have actual users.
>
>> And what about x86? --- irq 0 is used for timer and there is
>> void __init setup_default_timer_irq(void)
>> {
>>        setup_irq(0, &irq0);
>> }
>> in arch/x86/kernel/time.c.
>
> That's fine. There's no "irq" variable associated with it that people
> can test. No driver will ever see an irq number of zero, no dynamic
> irq code will ever see the zero.
>
> So x86 rules have always been that the way drivers etc test for irq
> existence has always been "irq 0 means no irq". Despite the fact that
> it internally uses irq0 for its own nefarious uses.

So can x86 please show the purely internal irq0 in its arch_show_interrupts(),
and accept "[PATCH] /proc/interrupts: irq zero is invalid"
(http://lkml.indiana.edu/hypermail/linux/kernel/1112.0/02229.html)?

Also, the several for_each_irq*() macros still iterate over zero, e.g.

# define for_each_irq_desc(irq, desc)                                   \
        for (irq = 0, desc = irq_to_desc(irq); irq < nr_irqs;           \
             irq++, desc = irq_to_desc(irq))                            \
                if (!desc)                                              \
                        ;                                               \
                else


# define for_each_irq_desc_reverse(irq, desc)                           \
        for (irq = nr_irqs - 1, desc = irq_to_desc(irq); irq >= 0;      \
             irq--, desc = irq_to_desc(irq))                            \
                if (!desc)                                              \
                        ;                                               \
                else

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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